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> There is a fantastic use for this, that if you don’t know, you may want to think about for more than a few seconds. Is it one of the things in the table towa

• geocar 4y ago
  > Is it one of the things in the table towards the bottom of the J article? Erm, no. That table suggests using b. as a replacement for other (clearer) algorithms for performance reasons, rather than parameterisation. What I mean by parameterisation is this: if you have a function that takes some arbitrary bitwise operation, instead of taking a lambda, you can pass the truth-table directly. This idea is mentioned only briefly in the J article (More Info, ¶2): 2. Operand m may be an array, in which case each result cell will be the array of the results of the logical functions specified by m. Maybe that is too-obvious to an array programmer and not-enough-obvious to someone who isn't, and so it is hard to properly consider the implications or applications of this. Here's one: Parsing AND/OR operations from an expression (like an SQL expression). You could use a tree of operators and then walk the tree for every row you want to consider or you could store the compositions as a list and do a single reduction. Is that enough for you to get the idea of what is going on here?
  • rawling 4y ago
    Ah, ok. I'd got as far as going, you can call "&","|" etc. a number based on its truth table, and then you can extend this to other operators we don't think about so much by completing the number range, but I hadn't got so far as going... what... a = (o >> (x + 2y)) % 2 or something. I'd hoped it might involve adding/multiplying different operators together or something like that.